1. Field of the Invention
The present invention relates to a laminated material and a laminated article such as a container and, more particularly, to a laminated material which is excellent in strength, toughness, thermal resistance, readiness to burn, punchability, and peelability from a lid member as well, and to a laminated article made out of such a laminated material.
2. Description of Related Art
Recently, in many cases, retort food is cooked as it is packed in a container by placing it in an electronic oven or in boiling water.
Such a container is heated while it still contains food therein so that a material for the container should have excellent properties with respect to thermal resistance, resistance to liquation, and oil resistance as well as a high mechanical strength and toughness. Additionally, the material should be readily burned from the viewpoint of pollution prevention and security of incinerators.
Heretofore, in order to meet with such requirements, for example, a resin composite sheet containing an inorganic filler has been thermally molded such as vacuum-molded or pressure molded or blow-molded to containers or a multi-layer sheet containing a resin composition layer with a large quantity of an inorganic filler and a resin layer with substantially no inorganic filler is molded to packing containers.
For example, Japanese Patent Kokai No. 264,478/1976 and Japanese Patent Kokoku No. 26,028/1985 disclose a packing container formed by a three layer sheet in which a high filler layer containing a larger quantity of a filler is interposed with a low filler layer containing no or a lesser quantity of a filler. This three-layer sheet is weak in adhesion between the layers so that when it is punched to packing containers, the prior art sheet causes filaments or whiskers on an edge of the container or the layers are likely to be delaminated.
Furthermore, Japanese Patent Kokai No. 63,283/1977, No. 15,963/1982 and No. 165,654/1984 disclose a sheet in which a layer containing no inorganic filler or an inorganic filler in an amount of 5% or lower is laminated on one surface or both surfaces of a high filler layer containing a larger quantity of the filler. This sheet is superior in surface characteristics, however, it is poor in adhesion between layers. When punched into containers, filaments or whiskers are caused to occur on an edge of the container and delamination is likely to cause. If a lid member is adhered to a container formed from the sheet as have been disclosed in the related publications, it cannot be peeled off readily because a peeling strength between the base material of the container and the lid member is smaller than the interface between the layers of the multi-layer sheet. If peeled off, the lid member may be broken or an inner layer constituting the container may be torn off.